Combustors of gas turbine engines are subjected to high temperatures and effusion holes can be used to direct air to cool combustor components such as combustor liner, dome and heat shield. Effusion holes extend through the component at a shallow angle with respect to the surface of the component, for efficiently cooling without risking a reduction in combustion temperature. Laser beam drilling of effusion holes in combustor components has confronted challenges. A combustor component is coated with a thermal barrier coating (TBC). Although a TBC layer is about 30% or less of, for example a heat shield thickness, it consumes more than 60% of the laser drilling energy, due to TBC properties such as heat resistance and poor thermal conductivity. Laser pulse energy is utilized to enable drilling through the TBC layer, but that laser pulse energy is too high for drilling through the base metal under the TBC, which causes excessive recast layer. The shallow angle of the effusion holes increases the distance which the laser beam has to drill through and increases the laser strike area on the component surface. This causes the intensity of the laser pulse to dissipate. Furthermore, shallow holes with an angle to the surface equal to or less than 20 degrees, may cause relatively long cracks at the interface between the TBC and the base metal. Crack length and the area subject to cracks increase as hole angle to surface decreases. Coating cracks are the main contributor to TBC spallation and chipping which risk part scrap or reduced part life in gas turbine engines.
Accordingly, there is a need to provide improvements.